CAMBRIDGE — The ailing grandmother of one of Matthew Slocum's alleged victims gave testimony Tuesday that might be used in Slocum's murder and arson trial next month.

Patricia McGarvin, Joshua O'Brien's maternal grandmother, said she gave O'Brien a cellphone on July 12. In the early morning hours of July 13, Slocum allegedly shot and killed O'Brien, his stepbrother, as well as Slocum's mother, Lisa Harrington, and stepfather, Dan Harrington. Slocum then set fire to the Harrington home in White Creek and fled, prosecutors allege. He was captured in New Hampshire with his girlfriend, Loretta Colegrove, and their infant son.

McGarvin testified Tuesday because it's possible she will be too ill to do so when Slocum's trial begins Feb. 27. If she is able, she will testify at the trial and the record made in court Tuesday will be discarded. If she can't be there, jurors will see a transcript of the proceeding and a video made in court. She appeared in the Cambridge Village Court instead of the County Court in Fort Edward because it is closer to her home in Hoosick.

Washington County District Attorney Kevin Kortright would not explain why McGarvin's testimony was important, but Slocum's lawyer, Michael Mecure, made comments that indicated police found the phone in Slocum's possession when he was arrested. Mecure said Slocum did not have the phone, and said whether or not McGarvin gave her grandson a phone was irrelevant.

Mecure said the police arrested the wrong suspect in the case, and laid blame for the killings on Colegrove.

There was a "conflicted family dynamic" in the Harrington home, Mecure said. Dan and Lisa Harrington didn't want Colegrove living there, he said.

The future of the case may depend on Judge Kelly McKeighan's ruling on whether statements Slocum made to police after his arrest will be allowed at his trial. At a hearing Jan. 6, police testified Slocum admitted to killing his family members and said Colegrove had nothing to do with it. Slocum took the stand and denied saying anything to investigators. Mecure said Tuesday anything his client said was obtained illegally.